[bepitulaz]

What

Every successful build123d build can now also produce a GRBL model.gcode for a desktop CNC. The assistant emits a machining plan (```camJSON block: material + face/drill/pocket/profile ops with toolbit ids), it is validated Elixir-side, and a FreeCAD 1.1--console` CAM job machines the exported STEP with the real toolbit geometry. The G-code appears as a "G-code (GRBL)" download next to STEP/STL/GLB; CAM notes/warnings render as an amber card in chat.

How it works

• Tool truth: mnft_cad/priv/cam/toolbits.json (feeds/plunge/RPM/stepdown per material, work envelope, post) + 24 vendored .fctb files from potsed/freecad_sainsmart_toolbits (Genmitsu MC40A flat ends 0.8–3.175, BN10A/MC40A ball noses, 20°/0.1 mm V-bit). Ball noses 1.2–3.0 mm are synthesized from same-size flat-end geometry (provenance noted in-file). Tune feeds by editing the JSON — no code change.
• Plan validation: Mnft.Cad.CamPlan — strict schema, toolbit ids must exist; rejection is non-fatal ("CAM plan rejected: …" note, model still lands).
• FreeCAD bridge: cad_worker/cam.py → cam_freecad.py. Geometry selection is deterministic (largest +Z face = top, +Z planar faces below it = pocket floors, full-circle edges = holes — the LLM never picks faces). Origin = stock min corner, Z0 = stock top. Ops clear their SetupSheet expression bindings so scripted depth/stepdown values stick.
• Honest output: G-code header lists tools/feeds/ops/warnings (oversized part, hole smaller than tool, undersized drilled holes, aluminum lube reminder). Missing FreeCAD / timeout / any CAM failure = chat note only; the model always lands.
• Timeouts: worker SIGALRM and the Elixir port deadline extend by the CAM budget so a 180 s CAM job isn't killed by the 60 s exec alarm.
• OpenSCAD: unchanged, mesh-only; the prompt says CNC export requires build123d.

Verification

• Elixir core 198/198, web 16/16, worker pytest 155/155 (16 new CamPlan cases, 11 new cam.py cases with FreeCAD mocked).
• E2E on the live pipeline (real LLM → build123d → FreeCAD):
  • aluminum 40×80×3 plate: plan {aluminum, face+drill+profile, flat-3.175}; G-code header rpm=10000 feed=340 plunge=140; four drills at exactly (6,6)/(34,6)/(34,74)/(6,74) through Z-3; perimeter profile with radius offset; feeds only 140/340.
  • "birch wood" phrasing → material=wood, feeds 900/300 @ 12000.
  • MNFT_ENGINE=openscad + CNC ask → no G-code, chat explains build123d requirement.

Deviations worth review

• V-bit: uses 20deg_V-Bit_0.100mm_Tip_MC50A.fctb (3.175 mm shank, 20°, 0.1 mm tip — exact match for the nano-blue bits) instead of the planned WC04A entry, which has a 6.35 mm shank that doesn't fit the 3.175 mm collet.
• FreeCAD ToolBit.from_file crashes on ° under the macOS C locale → the bridge uses ToolBit.from_dict after reading the JSON itself.

Config

MNFT_FREECAD_CMD (default the macOS bundle) and MNFT_CAM_TIMEOUT_S (default 180) — documented in .env.example and the README.